How wind can become a reliable source of power

2013-02-04 - Detractors of wind energy use a number of arguments to question its sustainability. One of them is that when the wind stops, back-up sources of power must be available at a moment’s notice to cover the shortfall. This duplication is inefficient and expensive, they say. This challenge is fast receding, says Alfredo Parres, who coordinates the wind activities of power and automation technology group ABB.

On the occasion of EWEA 2013, a major industry event, we asked Parres how he expects an unpredictable resource like wind to be turned into a reliable source of power:

Parres: A number of studies have shown that over a large geographical area wind output is pretty constant. If you take Europe as an example, the wind may not always be blowing in Germany, or Spain, or Italy, but it is always blowing somewhere. One solution is therefore to connect wind farms with each other and with the power network so that the constant output of wind over the catchment area becomes a constant output of electricity.

Offshore windfarm

Q: And how would this be done?

Parres: The way to do this is to build a power transmission network based on direct current. This solution is sometimes referred to as a “supergrid”. The idea has been around for a while but it hasn’t been feasible until now because a key switching technology that allows high-voltage DC lines to be interlinked or interrupted was missing. This gap has now been closed by the breaker developed by ABB last year.

Q: Why is this such a big step forward?

Parres: So far, there was no way to switch a high-voltage DC line off in a hurry. Without a method of breaking the power flow, a fault caused by a short-circuit could bring a grid to its knees. Actually what’s been missing is a method to break the current without causing significant and costly losses of electricity. The method to break HVDC developed by ABB last year promises to be both fast and economical. The other important thing about the breaker is that it allows nodes to be created so that DC power lines can be interlinked in a grid. So far, direct current transmission has mainly been used from one point to another.

Q: Is the supergrid a solution for onshore or offshore wind?

Parres: Both. When it comes to offshore, the typical solution today is to have a dedicated transmission line connecting each wind farm or small clusters of wind farms to the shore. An offshore DC grid would enable wind farms to be located further from shore and to be connected with each other at sea so that fewer transmission lines to shore are required. Similarly onshore, a supergrid will make it easier to aggregate the output of wind farms in a certain area and to transmit the power over long distances. The concept is central to the realization of visions such as Desertec, which aims to harness solar and wind power in Europe, North Africa and the Middle East and transmit it around these regions.

Q: What other benefits can the supergrid concept bring to the wind industry?

Parres: A supergrid would also help by allowing any excess wind power, or any other form of renewable power, to be transported to locations where it can be stored for later use. The only large scale and efficient storage mechanism today is pumped hydro, where electricity is used to pump water uphill to a reservoir from where it can later be released to produce hydropower. While we’re talking of storage, I should add that the development and deployment of more energy storage solutions will be another important contributor to the reliability of wind power, as will improvements in the capacity to forecast wind.

Q: So when will we get supergrids?

Parres: It will still take a number of years before supergrids are built. DC transmission is a well-developed technology that has been in use for 60 years, while the HVDC breaker is a research breakthrough that is still in the process of being developed into a product. Other reasons why it will take some time is that regulatory frameworks will have to be adapted to make cross-border supergrids possible and there are typically very long planning horizons in the power infrastructure sector. The development of an economically viable breaker, however, means that the planning for supergrids can now begin.